1. Field of the Invention
The present invention relates to a frequency generator in which a circuit wiring pattern and a generator coil pattern including generator wire elements connected by connecting wire elements, are formed on a printed wiring board.
2. Description of the Prior Art
Generally, frequency generators (FG) attached to various types of motors include both a frequency-generator magnetized section having magnetized portions circumferentially arranged, and a generator coil pattern disposed facing the FG magnetized section. The generator coil pattern, which is shaped like a ring, is formed on a printed wiring board (PWB). The coil pattern consists of a plurality of generator wire elements radially oriented, and connecting wire elements for connecting the generator wire elements into a series-connected wire. A predetermined circuit wiring pattern is also formed on the PWB.
The arrangement of the generator coil pattern and the circuit wiring pattern on the same PWB has been provided in various ways in conventional frequency generators, which are described below in brief.
In the conventional frequency generators shown in FIGS. 6(a) and 6(b), a generator coil pattern 2 and a circuit wiring pattern 3 are formed on opposite sides of a printed wiring board (PWB) 1, respectively. More specifically, the generator coil pattern 2 is formed on the obverse side of PWB 1 (FIG. 6(a)), and the wiring pattern 3 is formed on the reverse side (FIG. 6(b)). The patterns on both sides of PWB 1 are interconnected by way of through-holes (not shown).
In another frequency generator shown in FIG. 7, a generator coil pattern 2 and a circuit wiring pattern 3 are printed on the same side of a PWB 1. The circuit wiring pattern 3 is first printed on PWB 1; an undercoat is then applied over necessary portions of the resultant structure; and a generator coil pattern 2 is subsequently printed on the structure. Finally, an overcoat is applied over the previously applied generator coil pattern 2.
In an additional frequency generator shown in FIG. 8, a generator coil pattern 2 and a circuit wiring pattern 3 are also printed on one side of a PWB 1. In this construction, however, a part of the generator coil pattern 2 is omitted. That is, the generator coil pattern 2 is shaped like an arc, i.e., takes the form of an imperfect or discontinuous ring. The circuit wiring pattern 3 is partially laid in the omitted part of the coil pattern 2 on PWB 1 surface.
Those conventional frequency generators, whose circuit wiring pattern and generator coil pattern are formed as described above, have the disadvantages described below.
In the frequency generator whose coil pattern 2 and circuit wiring pattern 3 are formed respectively on the obverse and reverse sides of PWB 1 as shown in FIG. 6(a), through-holes 4 must be formed in PWB 1. Accordingly, a magnetic printed wiring board, such as an iron plate, cannot be used, and an additional piece, such as a back-yoke, for forming magnetic paths must be provided. Further, since the patterns must be formed in connection with the through-holes 4, chip parts cannot be used and therefore discrete parts must be used in place of the former. Accordingly, the parts used are expensive, and it is difficult to automate the mounting operation for these parts. The manufacturing cost of the frequency generator is therefore high.
In the frequency generator of FIG. 7 in which the coil pattern 2 and the wiring pattern 3 are printed on one side of PWB 1, the number of manufacturing steps is increased because of the additional steps needed to form the undercoat and the overcoat. This results in low production efficiency and high manufacturing costs. Additionally, during the printing of the patterns on the printed wiring board, resin phenol powder is produced when PWB 1 is cut, and this powder frequently disrupts the generator coil pattern 2.
The frequency generator of FIG. 8 in which some part of the generator coil pattern 2 is not printed, succeeds in solving the problems of low production efficiency and increased manufacturing cost, but creates other problems. Since some part of the coil pattern 2 is not printed, the output of the frequency generator, which is the sum of the outputs of the generator wire elements of the coil pattern 2, becomes correspondingly small. The wow and flutter of the FG output is also large.